Two Stroke Motocross
Two Stroke Motocross Forum => General Two Stroke Talk => Topic started by: YZ250 on July 16, 2010, 11:37:49 AM
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I've been wondering, for those of you who know what a rotary engine is, how come they haven't put them in dirtbikes at all? Theres been a few motorcycles with rotaries but i've never heard of any dirtbikes with them. Today it's all about saving emissions and fuel economy and such, and the rotary engine is perfect for that. It can produce more power than a piston and uses less fuel. If the dirtbike companies wanted to be more eco friendly they could mount a rotary engine in heir dirtbikes, or at least make a prototype, because then you'd have the power of both 4 stroke and the high end of 2 stroke, but you'd also have the fuel economy and emissions of a 4 stroke. All you would have to do is scale the engine down so that it would fit in the chassis, you wouldn't have to worry about the power to size ratio. It all makes sense and seems like a genius idea, so why haven't they done it yet?
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You probably mean Wankel engine, as a Rotary engine might refer to a piston engine where the pistons are arranged in a circle like in old aircraft engines, and yet, even these engines were used for a motorcycle :D. It looks something like this :
(http://www.bikernet.com/news/images/PhotoID20276.jpg)
Wankel engines have also been used in motorcycles, one that I've heard of was designed for road racing :
(http://image.sportrider.com/f/9819547/146_0803_12_z+norton_NRV588+wankel_rotary.jpg)
and actually, here's a dirt bike with a Wankel :D : Hercules Wankel GS
(http://www.southbayriders.com/forums/attachment.php?attachmentid=23098&d=1138552088]http://www.southbayriders.com/forums/attachment.php?attachmentid=23098&d=1138552088)
(http://img221.imageshack.us/img221/911/herculeswankel2ps4.jpg)
It would be really interesting to try this one out and see what it's like to ride. I suppose there might have been some issues with reliability maybe? That's just a guess though, I wonder why no one tried a Wankel engine in any newer motorcycles. Maybe the same reasons why Mazda is the only manufacturer using them in the automotive industry (could anybody more knowledgeable point out these reasons :D ? )
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That first one's not a rotary, it's a radial. The fact that someone put one on a motorcycle in inconceivably bad-ass.
By the way, rotaries don't use less fuel than a four-stroke; they're actually rather thirsty for their displacement. However, given that displacement, they do have some pretty immense power-producing balls, hence Mazda getting away with 1.3L motors. Here's what Wiki has to say.
The sealing at the Wankel apexes is less critical, as leakage is between adjacent chambers on adjacent strokes of the cycle, rather than to the crankcase. However, the less effective sealing of the Wankel is one factor reducing its efficiency, confining its success mainly to applications such as racing engines and sports vehicles where neither efficiency nor long engine life are major considerations. Comparison tests have shown that the Mazda's rotary powered RX-8 uses more fuel than heavier V-8 powered vehicles with over four times the displacement for similar performance results.
Also, the power advantage is a little controversial, because measuring displacement isn't as cut-and-dried as with a piston engine, so depending on how you measure it, they can appear way better than a four-stroke, or on-par with a four-stroke for power.
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The reason that they quit making them is that they ran on Pancake Batter and the riders didn't like having to skip breakfast.
http://leo_keller.tripod.com/Hersteller/Hercules/opendoor/opendoor.html (http://leo_keller.tripod.com/Hersteller/Hercules/opendoor/opendoor.html)
(http://www.southbayriders.com/forums/attachment.php?attachmentid=23103&d=1138552825)
(http://www.southbayriders.com/forums/attachment.php?attachmentid=23099&d=1138552169)
(http://www.speedtracktales.co.uk/mediac/400_0/media/DIR_78211/76_Fischer_Wankel_ZU.jpg)
"Kurt Fischer, Wankel the only rider to finish an ISDT (Hercules Wankel GS,) Gold Medal a very highly capable man."
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This is a rotary kart engine. http://www.woelfle-engineering.com/ (http://www.woelfle-engineering.com/)
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Go to Youtube and listen to a couple of the Norton rotary racebike videos.The sounds of those bikes sends a shiver up my spine.
A member of this site,Helmut Classen,has actually ridden the Hercules rotary I.S.D.T. dirtbikes and was very impressed by them.
Fichtel & Sachs also made Wankel snowmobile engines and even produced rotary chainsaws through their subsidiary Dolmar.
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Wankel rotary as opposed to rotary valve engines tend to make better top end HP rather than low end, for that a reed/rotary valve engine is far better.
I know there are 13B turbo engines in sleds :o 350HP !
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By "rotary" I meant Wankel. i just thought more people would know what i'm talking about if i just used the word rotary.
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Well, as long as we're going to make this thread a clusterfuck of different applications of the word "rotary," I suppose I should take this time to once again remind everyone that I am a big believer in rotary valve induction. I just got back from riding my own rotary-valve bike and even though it's got half the displacement, it's got the sort of crisp and immediate torque that my 250 (with reed valve) only wishes it could have. The 250's got about four times the top-end horsepower though.
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If there is anyone into radio controlled aircraft here, OS makes a small one.
(http://www.osengines.com/engines/osmg1401-b.jpg)
http://www.osengines.com/engines/osmg1401.html (http://www.osengines.com/engines/osmg1401.html)
Displacement: 0.30 cu in (4.97 cc)
Practical rpm: 2,500-18,000
Output: 1.27 hp @ 17,000 rpm
Weight: 11.8 oz (335 g)
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My buddy owns a Mazda RX-8, and it got me interested in the rotary engine so i spent some time lurking on an RX-8 forum. Even after decades of refinement, the RX-8 owners still say that the RX-8 shouldn't be used as a daily driver. It consumes too much gas (16-18mpg average) consumes oil (not a problem there ;-) and is high maintenance. I remember reading a couple of years ago a direct comparison of the RX-8 to a 350Z. While they produced similiar horsepower, the 350Z had nearly twice as much torque way down low.
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Isn't the RX-8 motor rated at 1.3 litres vs. 3.5 litres for the Nissan? My daily driver is a Mercedes running on a 50/50 Bio-diesel mix and displays longterm reliability that makes gas powered cars seem archaic.
I think it is fair to say that the Mazda Rotary serves it's intended market well.
I remember once having seen rotary powered fire pumps on a small ship and the Maintenance Engineer said they were the best.
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So, what you're saying is, the RX-8 is like a 125 and the 350Z is like a 250F? Except for the high-maintenance part, of course.
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It should be noted that the man who invented the Wankel engine that bears his name eventually went insane.Ah,so much to look forward to in life. :o
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It should be noted that the man who invented the Wankel engine that bears his name eventually went insane.Ah,so much to look forward to in life. :o
I think people around him Eventually figured out he was insane :D
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The Norton Rotary engined bikes did tremendously well in the 90s, in Britain. Winning British series and TT and Irish Road Races - Mainly with Steve Hislop riding them.
The new owner of Norton, took a Rotary to the Isle of Mann this year, but it was a rush job, them having got the rotary out of mothballs after he had acquired the company. Michael Dunlop (his dad, Robert, And his uncle,Joey, both raced the Nortons a couple of times, which few people know) was down to ride it, but after testing at the Jurby airfield, he / they felt it was too much of an ask to go out and risk things.
Hopefully, they come back with it next year. The new owner has stated the Rotaries will be further developed ( they were sold for a few years, as 588s, the never ending controversy of what the actual capacity of a rotary had them racing against 1000s etc, though I think the MOT classified it as 588cc).
I got to ride one of the very few 588s (perhaps the Only one) that came to OZ a few years ago. A beautiful handing bike ( alloy twin spar frame, I think made by Spondon) that went really well - especially if you regarded it as a 600 - that was the size / weight of it, and I personally believed it to be a sub 600 bike. It was a weapon. It's on my list of bikes I'd like to have in my workshop one day - hopefully they will go back into production. Though it will be hard to decide between a rotary and the new 965cc (?) parallel twin.
We've a young bloke along our street that drag races a Mazda Rotary ( Eastern Creek Raceway is only about 30 ks away, to get there it's 1 turn onto the expressway, then one turn into the road to the raceway, so even drag racers that can only go in straight lines have a chance of getting there....). Every now an then , he'll start it up, and do a bit of set up, drive down the road , wheelie bars and all, and do one loop around the block. The thing sounds outrageous, the young bloke doesn't keep on driving / revving it, so it doesn't drive the locals to their pitch forks. It's pretty cool, it puts a bloody great smile on my face when he fires it up. The best thing is if my brother is around - he bracket races a supercharged altered, with a Keith Black engine and Bruno trans ( and that's all I know about it - drags / car aren't much interest to me, but I do do a fair bit of fabrication for both my brothers drag cars and various street rods and classics), and he just about foams at the mouth when he hears a rotary. ;D It's a bit sad really, all my brothers care about are V8s , they have no interest in other stuff - limited imaginations, both of them, but I love 'em just the same.
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I have always been a fan of Rotary's.Had quite a few mates with them in the 80's.
RX2's & 3's with bridge port motors.It was quite a thrill doing 110mph in 3rd at 9000rpm down a country road when you are a teenager :D
1 friend built himself his own attempt at a pp motor. After watching him drive past work on its maiden voyage and not returning for quite awhile i new something was up. (We had our own standard test drive route).
Antony realised that ports big enough for the seals to fall out is not a great idea. ;) :(.
Anyway i see a couple of problems with a rotary in a dirt bike.
1: No one can decide what capacity to classify them as.
2: They make all their horspower at high rpm's.They do not have the mid range of say a 2 stroke.
While a rotary dirt bike with a cv transmission might make an interesting bike, I dont know if it would actually be a very good bike.
I saw the Nortons racing in the UK and they certainly where impressive sounding bikes.
Which reminds me, i must get all my old photos scaned someday.